A goblet contains $10$ red marbles, $4$ green marbles, and $6$ blue marbles. If a marble is randomly chosen, what is the probability that it is red?
Solution: There are $10 + 4 + 6 = 20$ marbles in the goblet. There are $10$ red marbles. The probability is $ \frac{10}{20} = \dfrac{1}{2}$.